@article {806, title = {Biallelic loss of function variants in SYT2 cause a treatable congenital onset presynaptic myasthenic syndrome.}, journal = {Am J Med Genet A}, volume = {182}, year = {2020}, month = {2020 10}, pages = {2272-2283}, abstract = {

Synaptotagmins are integral synaptic vesicle membrane proteins that function as calcium sensors and regulate neurotransmitter release at the presynaptic nerve terminal. Synaptotagmin-2 (SYT2), is the major isoform expressed at the neuromuscular junction. Recently, dominant missense variants in SYT2 have been reported as a rare cause of distal motor neuropathy and myasthenic syndrome, manifesting with stable or slowly progressive distal weakness of variable severity along with presynaptic NMJ impairment. These variants are thought to have a dominant-negative effect on synaptic vesicle exocytosis, although the precise pathomechanism remains to be elucidated. Here we report seven patients of five families, with biallelic loss of function variants in SYT2, clinically manifesting with a remarkably consistent phenotype of severe congenital onset hypotonia and weakness, with variable degrees of respiratory involvement. Electrodiagnostic findings were consistent with a presynaptic congenital myasthenic syndrome (CMS) in some. Treatment with an acetylcholinesterase inhibitor pursued in three patients showed clinical improvement with increased strength and function. This series further establishes SYT2 as a CMS-disease gene and expands its clinical and genetic spectrum to include recessive loss-of-function variants, manifesting as a severe congenital onset presynaptic CMS with potential treatment implications.

}, keywords = {Adolescent, Child, Child, Preschool, Female, Genetic Predisposition to Disease, Humans, Male, Muscle Hypotonia, Muscle Weakness, Mutation, Missense, Myasthenic Syndromes, Congenital, Pedigree, Phenotype, Synaptic Transmission, Synaptotagmin II}, issn = {1552-4833}, doi = {10.1002/ajmg.a.61765}, author = {Donkervoort, Sandra and Mohassel, Payam and Laugwitz, Lucia and Zaki, MAH S and Kamsteeg, Erik-Jan and Maroofian, Reza and Chao, Katherine R and Verschuuren-Bemelmans, Corien C and Horber, Veronka and Fock, Annemarie J M and McCarty, Riley M and Jain, Minal S and Biancavilla, Victoria and McMacken, Grace and Nalls, Matthew and Voermans, Nicol C and Elbendary, Hasnaa M and Snyder, Molly and Cai, Chunyu and Lehky, Tanya J and Stanley, Valentina and Iannaccone, Susan T and Foley, A Reghan and Lochm{\"u}ller, Hanns and Gleeson, Joseph and Houlden, Henry and Haack, Tobias B and Horvath, Rita and B{\"o}nnemann, Carsten G} } @article {756, title = {Congenital myasthenic syndrome with mild intellectual disability caused by a recurrent SLC25A1 variant.}, journal = {Eur J Hum Genet}, volume = {28}, year = {2020}, month = {2020 03}, pages = {373-377}, abstract = {

Congenital myasthenic syndromes (CMS) are a clinically and genetically heterogeneous group of disorders caused by mutations which lead to impaired neuromuscular transmission. SLC25A1 encodes a mitochondrial citrate carrier, associated mainly with the severe neurometabolic disease combined D-2- and L-2-hydroxyglutaric aciduria (D/L-2-HGA). We previously reported a single family with a homozygous missense variant in SLC25A1 with a phenotype restricted to relatively mild CMS with intellectual disability, but to date no additional cases of this CMS subtype had been reported. Here, we performed whole exome sequencing (WES) in three additional and unrelated families presenting with CMS and mild intellectual disability to identify the underlying causative gene. The WES analysis revealed the presence of a homozygous c.740G>A; p.(Arg247Gln) missense SLC25A1 variant, the same SLC25A1 variant as identified in the original family with this phenotype. Electron microscopy of muscle from two cases revealed enlarged and accumulated mitochondria. Haplotype analysis performed in two unrelated families suggested that this variant is a result of recurrent mutation and not a founder effect. This suggests that p.(Arg247Gln) is associated with a relatively mild CMS phenotype with subtle mitochondrial abnormalities, while other variants in this gene cause more severe neurometabolic disease. In conclusion, the p.(Arg247Gln) SLC25A1 variant should be considered in patients presenting with a presynaptic CMS phenotype, particularly with accompanying intellectual disability.

}, keywords = {Adult, Female, Haplotypes, Homozygote, Humans, Intellectual Disability, Male, Mitochondrial Proteins, Muscle, Skeletal, Mutation, Missense, Myasthenic Syndromes, Congenital, Organic Anion Transporters}, issn = {1476-5438}, doi = {10.1038/s41431-019-0506-2}, author = {Balaraju, Sunitha and Topf, Ana and McMacken, Grace and Kumar, Veeramani Preethish and Pechmann, Astrid and Roper, Helen and Vengalil, Seena and Polavarapu, Kiran and Nashi, Saraswati and MAHjan, Niranjan Prakash and Barbosa, Ines A and Deshpande, Charu and Taylor, Robert W and Cossins, Judith and Beeson, David and Laurie, Steven and Kirschner, Janbernd and Horvath, Rita and McFarland, Robert and Nalini, Atchayaram and Lochm{\"u}ller, Hanns} } @article {973, title = {Four Individuals with a Homozygous Mutation in Exon 1f of the Gene and Associated Myasthenic Features.}, journal = {Genes (Basel)}, volume = {11}, year = {2020}, month = {2020 06 27}, abstract = {

We identified the known c.1_9del mutation in the gene in four unrelated females from consanguineous families of Turkish origin. All individuals presented with slowly progressive limb-girdle weakness without any dermatological findings, and dystrophic changes observed in their muscle biopsies. Additionally, the neurological examination revealed ptosis, facial weakness, fatigability, and muscle cramps in all four cases. In two patients, repetitive nerve stimulation showed a borderline decrement and a high jitter was detected in all patients by single-fiber electromyography. Clinical improvement was observed after treatment with pyridostigmine and salbutamol was started. We further characterize the phenotype of patients with limb-girdle muscular dystrophy R17 clinically, by muscle magnetic resonance imaging (MRI) features and by describing a common 3.8 Mb haplotype in three individuals from the same geographical region. In addition, we review the neuromuscular symptoms associated with mutations and the role of plectin in the neuromuscular junction.

}, keywords = {Adolescent, Adult, Child, Exons, Female, Homozygote, Humans, Muscular Dystrophies, Limb-Girdle, Mutation, Myasthenic Syndromes, Congenital, Phenotype, Plectin}, issn = {2073-4425}, doi = {10.3390/genes11070716}, author = {Mroczek, Magdalena and Durmus, Hacer and Topf, Ana and Parman, Yesim and Straub, Volker} } @article {544, title = {A presynaptic congenital myasthenic syndrome attributed to a homozygous sequence variant in LAMA5.}, journal = {Ann N Y Acad Sci}, volume = {1413}, year = {2018}, month = {2018 02}, pages = {119-125}, abstract = {

We report a severe defect of neuromuscular transmission in a consanguineous patient with a homozygous variant in the laminin α5 subunit gene (LAMA5). The variant c.8046C > T (p.Arg2659Trp) is rare and has a predicted deleterious effect. The affected individual, who also carries a rare homozygous sequence variant in LAMA1, had normal cognitive function, but magnetic resonance brain imaging showed mild volume loss and periventricular T2 prolongation. Repetitive nerve stimulation at 2 Hz showed 50\% decrement of compound muscle action potential amplitudes but 250\% facilitation immediately after exercise, similar to that seen in Lambert-Eaton myasthenic syndrome. Endplate studies demonstrated a profound reduction of the endplate potential quantal content but normal amplitudes of miniature endplate potentials. Electron microscopy showed endplates with increased postsynaptic folding that were denuded or only partially occupied by small nerve terminals. Expression studies revealed that p.Arg2659Trp caused decreased binding of laminin α5 to SV2A and impaired laminin-521 cell adhesion and cell projection support in primary neuronal cultures. In summary, this report describing severe neuromuscular transmission failure in a patient with a LAMA5 mutation expands the list of phenotypes associated with defects in genes encoding α-laminins.

}, keywords = {Adult, Female, Humans, Lambert-Eaton Myasthenic Syndrome, Laminin, Motor Endplate, Myasthenic Syndromes, Congenital, Synaptic Transmission}, issn = {1749-6632}, doi = {10.1111/nyas.13585}, author = {Maselli, Ricardo A and Arredondo, Juan and V{\'a}zquez, Jessica and Chong, Jessica X and Bamshad, Michael J and Nickerson, Deborah A and Lara, Marian and Ng, Fiona and Lo, Victoria Lee and Pytel, Peter and McDonald, Craig M} } @article {362, title = {Presynaptic congenital myasthenic syndrome with a homozygous sequence variant in LAMA5 combines myopia, facial tics, and failure of neuromuscular transmission.}, journal = {Am J Med Genet A}, volume = {173}, year = {2017}, month = {2017 Aug}, pages = {2240-2245}, abstract = {

Defects in genes encoding the isoforms of the laminin alpha subunit have been linked to various phenotypic manifestations, including brain malformations, muscular dystrophy, ocular defects, cardiomyopathy, and skin abnormalities. We report here a severe defect of neuromuscular transmission in a consanguineous patient with a homozygous variant in the laminin alpha-5 subunit gene (LAMA5). The variant c.8046C>T (p.Arg2659Trp) is rare and has a predicted deleterious effect. The affected individual, who also carries a rare homozygous sequence variant in LAMA1, had muscle weakness, myopia, and facial tics. Magnetic resonance imaging of brain showed mild volume loss and periventricular T2 prolongation. Repetitive nerve stimulation revealed 50\% decrement of compound muscle action potential amplitudes and 250\% facilitation immediately after exercise, Endplate studies identified a profound reduction of the endplate potential quantal content and endplates with normal postsynaptic folding that were denuded or partially occupied by small nerve terminals. Expression studies revealed that p.Arg2659Trp caused decreased binding of laminin alpha-5 to SV2A and impaired laminin-521 cell-adhesion and cell projection support in primary neuronal cultures. In summary, this report describing severe neuromuscular transmission failure in a patient with a LAMA5 mutation expands the list of phenotypes associated with defects in genes encoding alpha-laminins.

}, keywords = {Adult, Face, Female, Homozygote, Humans, Laminin, Myasthenic Syndromes, Congenital, Myopia, Neuromuscular Junction Diseases, Tics, Young Adult}, issn = {1552-4833}, doi = {10.1002/ajmg.a.38291}, author = {Maselli, Ricardo A and Arredondo, Juan and V{\'a}zquez, Jessica and Chong, Jessica X and Bamshad, Michael J and Nickerson, Deborah A and Lara, Marian and Ng, Fiona and Lo, Victoria L and Pytel, Peter and McDonald, Craig M} } @article {534, title = {Variants in SLC18A3, vesicular acetylcholine transporter, cause congenital myasthenic syndrome.}, journal = {Neurology}, volume = {87}, year = {2016}, month = {2016 Oct 04}, pages = {1442-1448}, abstract = {

OBJECTIVE: To describe the clinical and genetic characteristics of presynaptic congenital myasthenic syndrome secondary to biallelic variants in SLC18A3.

METHODS: Individuals from 2 families were identified with biallelic variants in SLC18A3, the gene encoding the vesicular acetylcholine transporter (VAChT), through whole-exome sequencing.

RESULTS: The patients demonstrated features seen in presynaptic congenital myasthenic syndrome, including ptosis, ophthalmoplegia, fatigable weakness, apneic crises, and deterioration of symptoms in cold water for patient 1. Both patients demonstrated moderate clinical improvement on pyridostigmine. Patient 1 had a broader phenotype, including learning difficulties and left ventricular dysfunction. Electrophysiologic studies were typical for a presynaptic defect. Both patients showed profound electrodecrement on low-frequency repetitive stimulation followed by a prolonged period of postactivation exhaustion. In patient 1, this was unmasked only after isometric contraction, a recognized feature of presynaptic disease, emphasizing the importance of activation procedures.

CONCLUSIONS: VAChT is responsible for uptake of acetylcholine into presynaptic vesicles. The clinical and electrographic characteristics of the patients described are consistent with previously reported mouse models of VAChT deficiency. These findings make it very likely that defects in VAChT due to variants in SLC18A3 are a cause of congenital myasthenic syndrome in humans.

}, keywords = {Adolescent, Child, Diagnosis, Differential, Female, Genetic Variation, Humans, Male, Myasthenic Syndromes, Congenital, Vesicular Acetylcholine Transport Proteins}, issn = {1526-632X}, doi = {10.1212/WNL.0000000000003179}, author = {O{\textquoteright}Grady, Gina L and Verschuuren, Corien and Yuen, Michaela and Webster, Richard and Menezes, Manoj and Fock, Johanna M and Pride, Natalie and Best, Heather A and Benavides Damm, Tatiana and Turner, Christian and Lek, Monkol and Engel, Andrew G and North, Kathryn N and Clarke, Nigel F and MacArthur, Daniel G and Kamsteeg, Erik-Jan and Cooper, Sandra T} }